1. Field of the Invention
The present invention relates to an aircraft including a turbofan engine, and more particularly, to arrangement of an engine oil cooler and a pre-cooler.
2. Description of the Related Art
A turbofan engine of an aircraft includes a fan that is rotated by power produced by the engine. When the turbofan engine is operated, air is distributed into an engine body and a bypass flow path formed on the inner side of a nacelle. Air passing through the bypass flow path and air discharged from a nozzle of the engine body join together to be ejected backward. Thrust is obtained by the reaction of the jet stream.
Generally, the engine is equipped with various accessories, such as a fuel control unit, a fuel pump, an igniter, and a plurality of heat exchangers. The accessories are provided around, above and below the engine and the fan within the nacelle.
Examples of the accessories include a pre-cooler that cools bleed air from the engine so as to use the bleed air for a cabin air-conditioner or the like (Japanese Patent No. 4805352), and an engine oil cooler that cools engine oil.
Both the engine oil cooler and the pre-cooler are heat exchangers that use the air flowing through the bypass flow path (hereinafter, referred to as a fan stream) as a heat source (a low-temperature source) in the turbofan engine. The fan stream is sucked therein from the bypass flow path, and exhausted after heat exchange with the engine oil and the engine bleed air.
In order to sufficiently exert a heat exchange capacity, the engine oil cooler and the pre-cooler mounted to the turbofan engine are preferably provided at positions where the fan stream can be sufficiently introduced.
For example, it is assumed that the pre-cooler is provided in an upper portion within the bypass flow path of the engine body. In this case, the engine oil cooler is preferably arranged at a circumferentially different position from the pre-cooler, such as a position lateral to the engine body, so as to sufficiently introduce the fan stream therein without being disturbed by the pre-cooler.
However, in many cases, the engine oil cooler or the pre-cooler cannot be provided at a favorable position since its installation space is limited due to interference with another accessory or the like. Particularly, in medium and small aircrafts having a smaller engine size than that of a large aircraft, the accessories are concentrated around the engine body. Thus, the installation space is greatly limited.
When the fan stream is blocked by the engine oil cooler and the pre-cooler, smaller thrust is obtained, and fuel consumption is deteriorated.
Here, if the diameter of the nacelle is increased with respect to the diameter of the engine body, a required flow rate can be ensured. However, since it is necessary to ensure a height equal to or larger than a specified height between the nacelle and the ground, the diameter of the nacelle may not be enlarged in some cases. The nacelle diameter can be enlarged by increasing the length of a main landing gear. However, a weight increase is caused, and the fuel consumption is deteriorated.
Based on the above problems, an object of the present invention is to provide an aircraft including a turbofan engine which can secure a heat exchange capacity of each of an engine oil cooler and a pre-cooler while avoiding a deterioration in fuel consumption even when an accessory installation space is limited.